CROSS LINKING BY GAMMA RADIATION UNIFORM IRRADIATION METHOD

Transcription

1 IRaP CROSS LINKING BY GAMMA RADIATION UNIFORM IRRADIATION METHOD Hasan Alkan Ph.D, Tuğhan Özsezer and Hakan Behcan Gamma-Pak Sterilization A.Ş. İstanbul

2 IRaP Radiation Processing Cross Linking Radiation processing cross linking of thermoplastic polymers in order to enhance their mechanical, physical and also chemical properties. A well-known practice: heat and solvent resistance strengthen the molecular structure providing hydrostatic strength Cross linking with ionizing radiation (mostly e-beam) has been created an important sector in the world. Cables, plastic pipes, shrinkable tubes, washers, machine parts, lacquers, paints and thermoplastic adhesives

3 IRaP Aim of the Presentation Cross linking process under floor heating polyethylene pipes by gamma irradiation

4 IRaP Cross Linking of Polyethylene Pipes (PEX-C) Cross linking of PEX-C (polymers) can be achieved by either chemical or physical methods Chemical methods cross link ratio % * Type 1 (a) peroxide 75 Type 2 (b) hydrosilicon 65 Type 4 (d) nitrogen 60 Physical method Type 3 (c) PEX ionizing radiation 60 * Turkish Standard Institute (TSE) No: TS (1993) Methods mentioned (xylen solvent)

5 IRaP Cross Linking Reaction The most significant effect of ionizing radiation on monomers or polymers are due to the reactions of the free radicals during the irradiation. The polymer industry is based on free radical-initiated cross linking or degradation of polymer molecules. Fig.1 Cross linking reaction of PE molecules

6 IRaP GAMMA-PAK Gamma Irradiation Facility MSD NORDION JS MCi Co-60 total capacity Presently: 900 kci loaded Automatic tote box Wet storage type irradiator Tote box dimensions: 58x64x124 (h) cm Number of tote boxes: 64 / per badge

7 IRaP GAMMA-PAK Gamma Irradiation Facility Fig 2. Automatic tote box gamma irradiator

8 IRaP Dose Mapping Dose mapping perform with polywood but same effective density of the product Setting acrylic dosimeter in A, B and C cross section of the totes Fig 3. a) Tote box dimensions and dosimeter setting coordinates b) Dosimeter setting A,B,C cross sections; max-min points

9 IRaP Dose Mapping Fig 4. Dose distribution diagrams for A,B and C cross sections

10 Fig 5. Dose uniformity diagram (DUR: Dmax/Dmin) IRaP

11 Preparation of PE Pipes for Irradiation Loading the tote and dosimeter settings; Receiving the cross linkable PE Pipes from production companies Coiled and packaged in PE bags and nitrogen medium PE coils are m long 16 mm diameter For nitrogen medium companies made their own facilities Automatic vacuum cabinets, nitrogen supply system and hot wire sealing Nitrogen flash in the pipe and in the bag after hot wire sealing After receiving the pipe coils setting in 4/6 coils group and labeling Tote No. 1A, 1B, 1C, 1D 2A, 2B, 2C, 2D Loading the totes according to labeling arrangement 140 m coils 6 units per tote 160 m coils 4 units per tote IRaP

12 IRaP Coil Packages Fig 7. PE Pipe coil packages 160 m long (4 units per tote) Fig 8. PE Pipe coil packages 140 m long (6 units per tote)

13 IRaP Loading of The Totes Fig 6. Loading of the totes

14 IRaP Dosimeter and Settings For dose measurements; Harwell Acrylic Red Dosimeters used Measurement range: 5-50 kgys Each cycle dosimeter changes due to of range of dosimeter According to the dose mapping results; Max. Coordinates: Level 3 and 7. Dosimeter settings at level 7, at the beam coming direction outside of the coil Min. Coordinates: Level 1 and 9. Dosiemeter settings at level 1, inside of the coil at the sideway For monitoring the maximum and minimum doses; dosimeter settings made at the first, last and every 24 totes at the max. and min. coordinates Dosimeters moving with PE Pipe coils

15 IRaP Specific Irradiation Method of PE Pipe Coils According to our studies; To enable to achieve 60% of cross link ratio, the minimum dose must be delivered about kgys (TSE) To obtain min. 130 kgys; coiles are irradiated as 4 cycles Each cycles ave. 33 kgys delivered SPECIFIC METHOD: to achieve ave. 33 kgys; After PE coils irradiated 2 cycles; the places of coils are switched in the tote as; Replacement of coils from minimum to maximum and from maximum to minimum. And also the coils are turn around 90 in the tote. Doismeters moving with PE pipe coils.

16 IRaP Specific Irradiation Method of PE Pipe Coils Fig 9. Loading and replacement diagrams of PE coils

17 IRaP Results Before actual processing of the pipe coils; dose mapping is done with actual products (PE coils) in order to see the dose distribution to the PE coils in the tote. Table 1. Dose mapping of PE coils (actual product) Replacement of coils realized after second cycle Table 2. and 3. Actual processing of 160 m and 140 m long PE coils

18 Table 1 Dose mapping of PE coils (actual product) IRaP

19 IRaP Processing Number: PT Date: 12/04/2006 (160 m, 4 coils/tote ) CYCLE M.T. (sec.) INSIDE (kgy) OUTSIDE (kgy) OUT/IN 1. CYCLE 750 A/S B/F * 2. CYCLE 750 A/S B/F * 3. CYCLE 750 B/F A/S CYCLE 750 B/F A/S TOTAL , (11.4%) - Continuous Mode, Dosimeter results are average of 4 tote readings. - F: Front (beam direction) S: Side, A&B Level positions in the totes. *max/min ratio for regular irradiation Table 2. Gamma processing of 160 m PE coils

20 IRaP Processing Number: PT A Date: 03/05/2006 (140 m, 6 coils/tote ) CYCLE M.T. (sec.) INSIDE (kgy) OUTSIDE (kgy) OUT/IN 1. CYCLE 750 A/S B/F * 2. CYCLE 825 A/S B/F * 3. CYCLE 825 B/F A/S CYCLE 750 B/F A/S TOTAL (11.4%) - Continuous Mode, Dosimeter results are average of 4 tote readings. - F: Front (beam direction) S: Side, A&B Level positions in the totes. *max/min ratio for regular irradiation Table 3. Gamma processing of 140 m PE coils CrosLink ratio found: % (inner and outer samples) Analize Method:TSE (Xylen Solvent Method)

21 IRaP Conclusion To reach 60% cross linking ratio; For e-beam needs: kgys minimum For gamma needs: kgys maximum in nitrogen medium In regular processing; DUR max/min ratio = 1.41 (for 0.21gr/cm 3 density) Min. dose range: kgys Max. dose range: kgys In replacement method; DUR max/min ratio = 1.14 (for 0.21gr/cm 3 density) Min. dose range: kgys Max. dose range: kgys

22 IRaP Conclusion: Advantages Even providing the same minimum dose, the maximum dose obtained by this specific method is about kgys less Better dose distribution to the products Less chain scission / molecular degradation Better quality PEX-C products Saving about 25% time, energy and money

23 THANK YOU IRaP